I think this is very sad. At 19 years she is old enough to take on lots of grown up responsibilities like buying a home, getting married or having children but it seems she has not learnt how to be respectful. Maybe she has never been taught this while growing up ( you mention your daughter's mental health problems).
As hard as it maybe for you I would not send her money like that next time. I would wait till she contacts you or deigns to visit you then suggest that you go shopping with her to choose a present. If she makes excuses then say well we will postpone it till you do have time as I would like to spend some quality grandma time with you and maybe have a lunch treat too.
Absolutely do not let her walk away with money without consideration for you. Respect is one of lives valuable lessons and she needs to learn to show some.
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