I have Chase and I don't use the app but if I deposit a check either inside the bank or at the ATM I sign my name where it says endorse here.
I would write "For Deposit Only" and then you sign the check under that.
sign your name. Write her a separate thank you note
on the back you should sign your name on the top line and then add on the lines below like this:
SIGNATURE (yours)
For Deposit Only to
ACCOUNT NUMBER