I think it's okay to charge Grandma - especially if she offered to pay first - but I do think you need to talk to her about how much stuff costs now - I know I said this before - because she might be still thinking fabric costs $1.00 a yard - - - I don't know either of you, so - - -
I think a lot depends on the financial circumstances of you and Grandma.
If Grandma is quite well off, and you are hurting, this may be her way of getting something she would like for herself and helping you out, too.