Taking a bath in the "big tub" being scary is an issue for many kids, not just special needs kids. I think you need to be somewhat persistent about the transition if she is physically ready to do it or she will not do it. Making it fun as PPs have suggested is the way to do it.

My DS was the same way. Instead of getting a different tub, we replaced our fixed shower head with one that you can take off and use as a hand held one (it's really easy to do it yourself). He liked playing in the sprinkler and playing in the rain. We introduced it to him by asking him if he wanted to play in the indoor sprinkler. He willingly got into the tub. We turned it on really low (making sure the water was a good temperature for him - we also have a little space heater in there because he hates being cold, it's well away from the water and no danger). He liked it it a lot. Sometimes we use the stopper in the tub so it fills up a bit and he's okay with that. That was 4 years ago. He'll now freely take a shower but is still a little defensive when having his hair/face washed. You might think about it.

My ds had (and liked) an inflatable tub that looks like a duck. We got it at target (tho it's been a few years). I placed it in the tub, but only filled the duck. HTH. Good luck!

She will get used to it, really. You don't need another tub at this point.

Yes a few times.she did not like it

Have you tried the regular tub with really shallow water and a bunch of fun tub toys?

Dd is 2 and has finally outgrown the infant/toddler tub. She can sit up independently but doesn't seem comfortable doing so in the regular tub. Was thinking about maybe getting a little inflatable tub or something. Any suggestions/recommendations? Thanks