Identifying an aggresive molly?

[DevilDogs]

I want to begin by saying the two mollys I bought were labelled as dalmation mollys. After about 2 days of having them, one doubled in size and, after sexing them, we assumed the male had gotten her pregnant. We've had her 3 months now and she's still a little balloon. She's also picked up the habit of attacking the other fish. Primarily the two she attacks are a female betta and the male molly (we had axolotls that we had to remove bc she had started nipping at their feet as well). There are two plecos and two algae shrimp in the tank that as far as I'm aware she's never bothered. Is there any fool-proof way to tell just what kind she is and why she is so aggressive?

 

[Toad]

Any pics? Mollies can be little jerks, what size tank do you have them all in?

 

[DevilDogs]

This is the best picture of her I've ever gotten, but if you need more or specific angles let me know. Up until this passed Thursday, they were in a 55 gallon long. Currently, she is in a 15 gallon "emergency tank" after the 55 sprang a leak. It's only her, the betta, and one pleco in that tank. The other pleco and shrimp are in a 5 gallon since I didn't trust all of them being in such a small tank with her. Sadly, either due to the stress or the quick water change, the male molly has since died or I would give you a picture of him as well.

 

[Toad]

Well, she's definitely a dalmation molly, so it just may she is a jerk, although it will get worse in a smaller tank. Sometimes a 'time out' with her being separated and then reintroduced after a few weeks can work, but not always. At worst you may have to remove her permanently