Is there a specific Vanguard bond fund that is the "VTSAX" of bond funds?
I like and use VBTLX for this purpose.
Wellington and Wellesley are great funds, but they are IIRC balanced funds which contain both stocks and bonds. I prefer to do my asset allocation explicitly myself with pure stock and pure bond funds, rather than delegate that to the mutual fund managers - but that is just my personal preference.
What you could do is, with her permission, take a look at her current portfolio either manually or plugging it into a portfolio analyzer to find out what her current stock/bond/whatever allocation is.
Then you can replicate the same asset allocation with VTSAX, VBTLX, and maybe some other specialized funds if she owns TIPS or REITs or internationals or whatever and wants to maintain an investment in those types of things.
That way, she has the same investment mix, just at a lower cost.
Be careful! If her investments are in a taxable account, she might very well incur a large tax penalty if she switches investments. If this is the case, then what you can do is transfer the assets "in kind" to a place like Vanguard. The fees associated with the investments themselves would continue, but the advisor fee would stop.