can I deduct medical expenses my daughter incurred but that I paid for on her behalf?

[bjmanasco]

she is an adult so I cannot claim her as a dependent

[DoninGA]

Yes, you can enter those medical expenses you paid for your daughter on your tax return as medical expense itemized deduction, along with your own medical expenses.

See IRS Schedule A page 2 - https://www.irs.gov/pub/irs-pdf/i1040sca.pdf

Whose medical and dental expenses can you include?

Any person you could have claimed as a dependent on your return except that person received $5,200 or more of gross income or filed a joint return.

[Bsch4477]

Depends on her income. You can only claim the costs for a dependent or someone who could have been a dependent but they had gross income greater than $5,200.