OMG NO!! What on earth did A QUALIFIED THERAPIST suggest that for!?! I really don't think she is going to be alright with that, at all!! If you buy a big enough one and she actually hits you with it, when you present it as a solution to her sexual issue with reservedness, it could black your eye! lol
Plus sex toys are an acquired taste imo and don't always produce arousal or orgasmic results in people who enjoy sex.

Wouldn't you be better off looking for instructions on good techniques, the different parts of the vagina that are most responsive to different stimulations, and little tips and tricks to help her achieve orgasm? Then, equip with this knowledge, begin talking to her again about it all and if she would want to try the next time you have intercourse? x