I had a severe reaction to Bactrim that didn't start until after I had been on it for a couple weeks for a sinus infection. It started with a mild rash and then eventually progressed to anaphylaxis & a sjs rash that took weeks to completely heal. Since her dose was recently doubled and allergic reactions can develop at any time I wouldn't rule out a drug reaction. If her symptoms do not completely resolve very soon- especially if she develops any redness or swelling around any areas of her face, mucous membranes or any fever- I'd call the dr. Better to be safe!!