I knew it! I just had a feeling Tara Strong wouldn't be voicing her, and I was right!..
I guess she's too busy at the moment with things like "My Little Pony", "Teen Titans Go!", and goodness knows how many other projects she's been involved in. OR, maybe IG don't have as much budget as in previous games; since Tara Strong is quite a popular voice actor, she's probably quite expensive to hire and IG knew they should keep their VO budget for their regulars like J.A.T, David Kaye and Jim Ward, since they've all been in the franchise since forever and it would probably have been a bigger loss if they hadn't brought back any of them…
I don't know if either of these theories are true - it's just aimless speculation as to potential reasons why she isn't coming back for "Into the Nexus", but, whatever the actual reason, I hope the new Voice Actor lives up to the standards set by the Ratchet fandom - let's not forget from how poorly A4O and FFA were received, that many people in this fandom can be very nitpicky…