Molly McGrath

When Molly reappears in the 2013 rebooted series, Nicole Oliver (who also played Forge Ferrus' daughter, Jet, in the previous continuity) voices her. Nicole is definitely no stranger to portraying the mothers of various animated characters throughout her career, and Molly goes to show why. She's got that perfect soothing, motherly voice and performance. 

For Molly's final and brief appearance in Team Turbo, an uncredited Lili Beaudoin voices Molly. This was presumably because the franchise was moving on from these established characters like Molly, and Lili was the only voice actress in the cast (as she was also playing Rayne Martinez, who would be a key player later in the movie). Might as well have her pull double-duty for this minor role instead of bringing Nicole back for only a handful of lines. The unfortunate thing is that Lili's voice for Molly is pretty much just a slightly-less-high-pitched version of her Rayne. Luckily the two characters never interact, and are separated by almost an entire act in the movie, because otherwise that would've been awkward...

Nicole is obviously taking my vote. The Unknown Voice Actress is serviceable and Lili would've done better with more material/in a series where she wasn't trying to voicematch Nicole's version of the character.