is it normal for a partner to masterbate just as much or more than your having intimate relations with them?

i work full time. my sex with my partner is wonderful, passionate & satisfing on both parts. but she masterbates more than we have sex while i'm at work then hides it from me. i know masterbation is healthy but just as much or even more than we make love. I feel if the relationship is so satisfying whats the need to do this so often.
are there others out there who feel left out or uncomfortable about this?