She currently has a Samsung Galaxy S5 on Verizon Wireless. I explored their international options and they want like $40 for 100 minutes and 100 sent texts. It's an option but I don't even know how that would work over there. It's a CDMA phone and from what I read online, India has a GSM network.
The same way KnowRoaming works over there, they're roaming onto GSM networks using the GSM/LTE network support on the phone.
Here's the specs on the Galaxy S5 - note the support for GSM 900/1800 bands and WCDMA (HSPA) 900/2100 bands which are all GSM bands used in India. Verizon might be a CDMA network, but LTE technology is GSM-based (thus the SIM cards for LTE service), and the LTE band that Verizon bought in the United States from the FCC for service requires the SIM slot be carrier unlocked. This means you can buy the KnowRoaming SIM sticker, apply it over the Verizon SIM card, put it back in the phone, and install the KnowRoaming app to toggle between Verizon and KnowRoaming any time you like. It's a bit of a chunk of change up front ($30), but it comes with $10 in airtime, and PAYGO through KnowRoaming at around 21-25˘/minute/SMS/MB (depending on destination and service - it's cheaper/more expensive depending on the country) may not be much cheaper than Verizon's roaming package in India, but it's PAYGO and it comes with data access and free incoming texts as well. What she doesn't use in credit can be saved for another trip later as unused balance rolls over for as long as 15 months of account inactivity. She even has the option of setting KnowRoaming up to have her Verizon calls forwarded to their roaming service.
This will probably be cheaper and more convenient in the bigger picture than shopping for a burner phone over there, but even if you want to go that route, she can still just pick up a local SIM card and stick it in her existing smartphone and still have it work with no muss and fuss, she just has to pull her Verizon SIM and switch over to GSM network service in the phone settings menu. But it'll work for the same reason that Verizon can roam in India without a CDMA network and why I recommended KnowRoaming as a good international roaming option. No sense generating more electronic waste. Trust me, I'm smarter than your average bear with this stuff.
And for the record, it also means that that shiny Galaxy S5 could be taken to any AT&T or T-Mobile based MVNO here in the States to potentially save money as well (not just Verizon MVNOs like Selectel), and still do the same KnowRoaming trick to enable international roaming support.