Nâh.. I don't think Bud envies Shelly.
Bud just realized that her sense of guilt overpowered her reason again for a bit. Her "thing" for Justin, was just puppy-love, and a bit of experimentation with flirting that panned-out the wrong way....
After all, Bud might be véry old, she's still physically a teen. (Sort of frightening, being stuck with teen-anxt for millenia..

Above that, Bud takes her role as M's guardian pretty serious. It has become her main purpose. Sort of an endearing attempt to redeem herself.
The interesting thing is the difference between The Golem-Girls in dealing with their guilt. Bud has always been pretty open about her guilt. Brandi bottled it up, unable to express her true feelings, unsure as she is about how to react to other people if she blurts all out, and gets a reaction (aspergers are like that) . Brandi tends to keep mum, because the outbursts of emotion that she would invoke, fill her with a deep dread. Unable as she is to correctly process, said, emotions.
Jin, on the other hand, has actively redeemed herself by diving head-deep into major historical manipulation to set wrongs right. Something that I think, Bud is somewhat envious of. Hence their continuous head-butting. Adding to that Jin's 'humanization" and one can imagine the turmoil inside of Bud.