The simple answer is use ‘with’ not ‘at’. There are several alternatives you could also use such as: - she is not au fait with technology - she is not tech savvy - she is a bit of a Luddite - technology is not her forte - technology is not her strong suit - technology baffles her Please note: these alternatives use a higher level of English so if you are unfamiliar with these expressions simply use the first option. There is no need to use big words simply for the sake of it when the meaning is the same. Additionally, some of these carry a negative connotation (Luddite) which you may not wish to convey.

"bad with"

my granny isn't tech savvy.

She is useless with... She really can't handle... She can't get her head around... .... are beyond her ... are not her cup of tea (?)

My grandma is not savvy at using a computer, a smart phone or any modern technology.