Please consider that the problem might not be the harness itself, but how you act with the harness.
Chihuahuas are small dogs and can be slinky when they want to avoid something. If you grab her, lift her up and somehow force her into the harness, that process is very uncomfortable. Even if you don't cause her any pain, it's still uncomfortable from a psychological point of view to be robbed of your ability to escape.
The way I often see people put a harness on their dog is: standing with their legs fully stretched, bending at the waist to reach for the dog and grabbing or pulling the dog if it doesn't stand still and in some cases even trapping the dog between their legs.
In short: people are towering over their dogs, which is a very aggressive pose in dog's body language. And since many dogs want to avoid this aggressive situation, people become even more aggressive or physically rough to just get the darn harness on.
A much better pose is to kneel or sit down and offer the harness to the dog with outstretched hands. If the harness (or coat) needs to go over the head, you should hold it in a way that the dog can simply walk into it. To train this behavior, hold a treat behind the hole to lure the dog into the harness voluntarily.
If kneeling down isn't an option for you, you could have the dog jump on your lap to avoid the towering pose.
If the legs need to go into holes, the process is a little more complicated, but still works best without applying any force. Having their feet lifted from the ground can be disorienting for dogs. So it's better to stroke the fur from shoulder to the foot to give the dog time to either lift the foot themselves or to mentally prepare for having the foot lifted.
Maintaining a calm chat of encouragements and praises also helps convey the message that this isn't an aggressive situation. If your dog is very nervous or too hyped up, you should speak with an extremely low and calm voice to calm your dog.
In your specific situation you could start a harness desensitization training. Right now your dog connects the harness with negative memories, so she hates the sight of it. By connecting the harness with positive experiences, you can change her mind.
If you already have different harnesses, I highly recommend doing the training with a different harness than you use for walking.
Get the harness out several times a day (without actually going on a walk) and offer a treat in the close proximity of it. Your dog should simply come to you and eat the treat. After that you simply put the harness away again. It may take a few tries at first before she even takes the treat, but eventually she will trust that she can eat it without having to put the harness on.
Once she reliably takes the treat, you can adapt the training to make her put her head through the harness in order to take the treat. A few days after she started doing that reliably, you can start putting her legs through the holes and rewarding her with a second treat, but still without closing the clasps and going out.
Only when she voluntarily puts her head into the harness and you can calmly put her legs through the holes should you switch to using the training harness for your actual walks.