I've got a story for you that may not offer a whole lot of comfort,but perhaps it is still worth reading. I think it may help for some experience perspective. First, I will say that simply ignoring the problem as best as you can may be your best bet. It will likely work itself out after no too long. About a year ago my son (then 3) had a fire alarm test at his daycare. He was never scared of ANYTHING at all ever...no matter how loud or anything. He saw the other kids scared and realized that all his friends were scared, so he should be too. He became deathly afraid of all the ceiling vents in our house (the ones the air comes out of from the gas furnace were the worst, but also fire alarms...anything in the ceiling). He wouldn't go in the bathroom for 2 or 3 months (good bye potty training progress). We tried many times to point them out and explain what they did/show him what they did so that he would not be afraid of them. The only thing that did was solidify the fear and set it in stone. It ended up being about 3 or 4 months before he was not afraid to even set foot in the bathroom. One night, just as he was starting to feel comfortable getting in the tub and walking into the bathroom without one of us there, a spider in the bathtub startled me. I am not afraid of them, but since it startled me, I screamed and jumped. Today, when he sees a spider, he freezes and cries until we go and get him and walk him past it...even if it only looks like one or he thinks there could be a spider there when there really isnt any at all.
The moral of the story is that I think the fears of others, myself included only made things worse. His friends taught him to be afraid of things. Now, I cannot say that he would have never been scared of anything because everybody is scared of some things and at around the age of 3, the imagination begins working very well and kids imagine all kinds of scary things that could never happen. You may be better simply acknowledging her fear and doing your best to let it rest until she is over it. In my personal experience, trying to explain that things were okay only reminded my son that it was scary and made him even more scared. Another thing you might try, since your daughter is likely imagining the bubbles coming on (or perhaps something even more scary) is helping her to imagine safe things...things she knows cannot hurt her...that way her mind is not clouded with things she percieves as scary. Good luck. Fears at this age due to a traumatic event of sorts are very difficult to deal with.