Bella sounds confused! It seems like she doesn't have any clear "doggy" rules (rules that make sense to her) so she is beginning to make her own! Lady Bella needs some clear boundaries (places she understands the meaning of) so she can navigate around them and be rewarded for doing it right!
You're absolutely correct in your assumption that "bad attention" is just as good as "good attention!" (in some dog's minds when they form habits like it sounds like she's forming.) Bella is most definitely doing those things to get reactions. Chihuahuas are INCREDIBLY intelligent and so so eager to please and be rewarded, and when they are not "challenged" they will do anything and everything for attention and direction... and usually that means making up their own rules!
Using the crate as a potty area is confusing her. When you put her in a crate, that is working on your dog's instinctual notion of a "den." And a den is not where we potty. A den is for safety and relaxation. Putting out too many pee pads will also confuse her. Dogs are territorial and understand their surroundings based on "there is a place for everything." If you give her too much, she will be confused and say to herself, "Well, these humans are just letting me have everything! I need to know where exactly I'm supposed to do things, so I guess I'll just decide myself!" (this is where the aggression/territorialness is coming from.) Potty training is especially difficult for a small dog because our house is SO LARGE, when they potty in a corner or in a bathroom they feel like that's OK because it is FAR away from their food and our communal space.
First of all: STOP WORRYING!
The last thing you want is anxiety about training or what habits she's forming. The most wonderful thing about chihuahuas is: They don't do a lot of damage! When miscommunications, bad habits or accidents happen they're usually so small and minimal that it's very easy to fix them, so the added stress and anxiety is not needed. Lady Bella is a smart and observant little girl, and she'll absolutely flourish if you start giving her some outlets to release her energy! She wants to please you and be a part of the family!
I am also a stay-at-home wife with 3 dogs and it's so wonderful to be able to give them the time they need to be fulfilled.
If you don't already have 20-30 minutes of training time (a time where she can learn new tricks, brush up on her old ones, and make you happy) please start. It's important that every day you give her a place so all her "I WANT TO PLEASE YOU!!!" energy is put in it's proper place... instead of "Pay attention to meeeeee!" which is what happens when she lashes out. I have 3 dogs:
... and I have to work with them every single day for at LEAST 30 minutes, and help them know that they have a "job" and a place in the family. Dogs have to work. We brought them into our homes because we needed them to do something, and if a dog doesn't have a job... well, then you're going to have all sorts of problems. Take 30-40 minutes a day with Lady Bella to show her that she is acknowledged, she has to work for affection (honestly, receiving something you worked for feels way better than just a "gift," right?) and that you are the person she needs to trust and respect. The territorial habits Lady Bella is forming are not good for her because she feels like she needs to tell everyone what to do. And what does that do? Causes stress. It would be like you going into a job and everyone saying, "Well, what do YOU want to do?" You wouldn't have the first clue! Working on Lady Bella's training each and every day will lessen her stress and her need to set the rules. You set the rules. You're the human! You know about doorbells, cars, mailmen, telephones and strangers. You know those things way better than Lady Bella ever will. And she needs to know that.
As for the potty training, I always suggest a strict "outside is for potty, inside is not" rule. This has just always been the most direct and clear way (for me) to communicate to my dogs that I don't want them to potty inside. At all. BUT... I do have a pine shavings litter box in my garage for my chi because I live in Colorado, USA and in the winter there's upwards of 3' of snow... impossible for my chi to potty in!
Hope this helped! Good luck!