I went to Merial's website, but under side effects all I saw listed was a skin reaction:
http://frontline.us.merial.com/produ...s_faqs.asp#q16
You are using the one that is appropriate for her size, right? If she's super tiny, using the spray so you can customize the dose would be safer.
Of course, if you've noticed a connection, I'd stop using it and switch to something else.