Not sure she can deduct them. IRS PUB 502 specifies situations where you can deduct medical expenses paid for others. This includes anyone who qualifies as the taxpayer's dependent (qualifying child or relative).
You can include medical expenses you paid for an individual that would have been your dependent except that:
1. The person received gross income of $4,700 or more in 2023;
2. The person filed a joint return for 2023; or
3. You, or your spouse if filing jointly, could be claimed as a dependent on someone else's 2023 return.
The publication is silent on your situation.
If she can it raises the question of the need for you to file a gift tax return if the amount was over $17,000 in 2023.
perhaps in the future, if this situation continues, gift her the money and let her pay the bills directly. This would still require you to file a gift tax return if the amount you gift her is over the return filing threshold. You may ask why there may be different results because of who directly pays the expenses. A gift of money allows her to spend it any way she chooses - pay the bills or buy a car.
