I am pretty sensitive to stims, so I have found green tea extract and ALRI Venom Hyperdrive to be a good combo. Assuming her diet and training/cardio is set up to facilitate fat loss, this will be a good boost.
Something a little harsher, yet effective and legal, would be ephedrine/caffeine.
I have found Synthetek's synthetine/syntheselen combo to really assist in melting fat, but she may not be into the method of administration for those.
Most other OTC fatburners I have tried over the years have caused too much anxiety.