I am so sorry about your mom. That is wonderful that even in this time, she's thinking of those she loves and trying to make it as easy as possible on you and your sibling.
I lost my dad a few years back, and there were several accounts (401k, IRAs, life insurance policies) and a small house (our childhood home). I have one sibling and he split everything 50/50 in the will.
Whomever is named executor/trix should be moderately comfortable dealing with money and paperwork. And if there is the possibility of animosity between siblings, an outside person might be best so one is not seen to be favored above the other. But if you are taking it on, I might want to say please consider not taking the executor's fee from the estate as a gift to your sibling since it would be unbalancing the "equal" division. But if you feel it is going to be a huge amount of work, then that is what the fee is for... I just point this out because if you have the least little bit of difficulties with your sibling, it would be so sad for the fee to cause more problems and it may not be worth it.
We had dad's tax guy/attorney as a guide through all of this, and he advised us on any legalities and the steps involved for our state. Definitely recommend finding one that is reasonable as he was invaluable for us - including filing the final both our father's taxes for his last year and the estate taxes (it drug out over 2 years) and making sure to get the forms needed to us after closing the estate.
One thing that really helped was that on several of his investment/retirement accounts, dad named us as Transfer On Death beneficiaries. Also known as TOD, you can put in any percentage. I believe they even allowed "per stipes" which means in the event that one beneficiary has passed, their children will still inherit their parent's share (only important if either of you have children obviously).
Anything labeled TOD or with beneficiaries, means it passes outside of probate (but may not avoid state estate taxes if your state has them). This designation trumps anything in a will, which means also that even if she wants to leave 100K to a charity or whatever, if she's named you and sister as TOD beneficiaries on her investments, that will bequest will need to come from the estate - cash/bank account with no beneficiary named or funds from after the property is sold if not specifically named "I leave the house to my son and daughter" type of thing - but that is why you need an attorney to write a will correctly. So she should be aware that any gifts to other relatives or charity need real money/property sold to back that up otherwise it might not be fulfilled.
She may want to make all of her charitable donations now while she is still alive and just leave a simple will - you and your sister as 50/50 heirs, all property to be split between you, and any investment accounts that can have named beneficiaries, do so. This would probably be the easiest for you and your sister as long as you get along well.
Again, something to discuss with an estate planning professional - how to ensure the stuff she wants gets done in her will.
For the investment/retirement beneficiary designations, that money is released to you and your sister as soon as you satisfy their requirements and is not required to go to probate. The financial institutions will walk you through the steps involved, and you should make sure to let them know this applies to you and your sibling (she will need to contact them after the fact as well, but most of the time did not need to send additional death certificates - they should assign you a contact that can match you both up with your parent's accounts and advise you both how to proceed with setting up your inherited accounts). But basically you'll call up each one and get them to tell you what they want from you.
Fido allows you to set beneficiaries online, and I'm pretty sure most other places allow this as well, but first setup would be to contact the financial institutions and ask if you are unsure.
Same for any life insurance policy. My dad's had a feature that allowed the funeral home to take their expenses directly from the policy and then cut us a check for the remainder (as sister and I were equal beneficiaries, we received a check for half of the remainder and it was already calculated on there how much in taxes we'd owe for the interest earned for the time between his death and the final payout).
The property went through probate, and you definitely should make sure that happens. You and sister can declare a set value on the contents (furniture, antiques, books, clothes, vehicle...) instead of having to have someone come in and value it for a price and take ages to do so - at least that was an option we were given, and we chose to do so to save time and anguish going through everything (but we also were dealing with a hoarder, so that would have been awful). Unless your mom specifies items in her will for certain people, that would mean you and your sister would just pick things you want and agree how to deal with the rest on your own (and can give away items for her as long as she leaves you a list? Seems easier if you all get along, but if not, then she'll need to name things in her will so there is no misinterpreting).
As far as the house you really want to make sure it goes through probate since by inheriting, you get to reset the value at the time of your mother's death - it is called "stepped up cost." So that means that if she paid $50K for the house back in 1980, and it is now worth 200K, if she gave you the house before death, you would have to pay taxes on the increased value of $150K (split between siblings if sold and you're equal partners). But with inheriting it through the magic of stepped up cost, you take the current house value on the date she dies (can use property tax records or have a realtor evaluation - we used prop tax records ourselves for the year he died). Therefore if you sold it and got $220K, you'd only have to split the extra 20K for your taxes. And if you sold it for 180K, then you'd get to write off a loss on your taxes of 20K... so it's VERY important to check with a lawyer to make sure this happens correctly... the difference can be painful if the house has appreciated quite a bit since purchased and that would suck to get hit with a several thousand tax bill because it wasn't properly setup through inheritance.
The accountant (if you have one and I do recommend it for the estate anyway if not for your mother's final tax bill) can be paid out of the estate. They will send you and your sister any and all forms and tax statements necessary (things like 1099-INT, 1099-DIV and K-1 forms).