Assuming that your daughter holds a British (or other EU) passport, you'll have no problems. The Canary Islands are Spanish territory, and thus part of the EU (even though they have special tax status, which means they count as 'non-EU' when bringing back tobacco, booze and souvenirs).
All EU member states are obliged to admit anyone who can prove their citizenship (with a valid passport or national ID card). Immigration officials, throughout the EU, must accept your daughter's passport, right up to the last second of the day on which it expires.
However, if your daughter's passport is renewed now, any unexpired time will be added to the validity of her new passport.
Chris