I don't know anything about Extella, but given it was a mission to recover her husband I would give it a pass on how evil of things she could do. Tamamo has always been willing to do horrible evil things if it's for advancing her own desires. She is neutral evil, after all. The difference is she doesn't want to do evil for evil sake, but only when it brings her closer to her own happiness, which usually follows the theme of involving satisfying her spouse. Like a mother willing to pull a gun on her child's bully she doesn't tend to hold back with wanting to push people down stairs either. So why do I give it a pass? Because performing these terrible deeds requires a trigger to want to do them, and if she doesn't need to do them she obviously won't.

However, even if hypothetically in a scenario Tamamo wanted to build an army for evil and conquer to conquer the world for her and Rits, do you actually believe Rits wouldn't tell her to stop? Which would go against the whole reason for the conquest in the first place, thus making it invalid. There is just no actual scenario she goes to enact some horrible deeds while he sits back, watches, and does nothing.

Also Beni's comment that Tamamo would fatten her husband by smothering him with affection is not 100% accurate. (Especially since the section it came from was rather built for cooking show humor than deep character writing.) The whole idea is that she focuses too heavily on their favorites, and would want to spoil them soon heavily. My counter arguement to Beni's would be in Tamamo's bond 10 book where it states that the perfect wife both spoils their spouse and let's their spouse spoil them. Implying there does still need to be more to it than onesidedly letting her do everything into the marriage for the rest of time. She will want to spoil her children and spouse, but the phrase wise mother and good wife has to imply to some level she would be wise to some level involving taking care of her family's needs appropriately.