Thickening definitly helps! What formula is she on now? If it's a normal cows milk based formula you could consider changing to a reflux formula. My two are both refluxers and had a combination of ranitadine and Enfamil AR. Reflux formulas are either thicker in the bottle or (like the one we used) thicken in the stomach, they are available on prescription or can be bought from a pharmacy. SMA do one called staydown. We had great success with the formula, my two did well on it and DD still has one bottle a day at bedtime.
If she is on a hypoallergenic or soy formla there are thickeners available - again on prescription or you can buy them in a pharmacy (may need to be ordered in and the formulas will), carobel is one that's available in the UK. These you add to the bottle to make a consistency that suits your LO. With the formulas and thickeners you will need a fster flow teat.
Many reflux babies in the UK (I'm assuming you are UK!) start with infant gaviscon which is a stomach stabiliser which also works as a feed thickener.
What medication is she on now, how heavy is she and what dose is she on?
HTH!
Laura