try to get one of those uv sun suits for her to wear - they save you having to re-apply the sunscreen everywhere quite so often. Take a few hats with a wide brim to sheild her eyes.
be careful if you try to change a nappy on the beach - you always end up with sand in it stuck to their bottom!
Try to chill and relax - it is actually a good age to take them, as you can take her out in the evening in her buggy (take a blanket) and if she feels like a sleep, just let her and you can sit and relax with a glass of wine and enjoy your evening.
Whilst a healthy diet is important, don't give yourself grief if all she wants to eat is bread and butter for a week, you can get back to normal when you get home. take dry snacks for the plane - my kids always liked little bags of cheerios.
Take a mini medical kit - sachets of calpol, nurifen, some piriton, rehydration sachets, plasters, disinfectant etc.
Make sure that you get you european health cover cards.
Unless your daughter has any skin allergies, just get a high factor sunscreen appropriate for kids. I always get a sensitive skin one anyway - check out how runny it is, some a quite thick and hard to apply.
best of all, just try to chill out and relax and nyouy your holiday.
Above all, try to enjoy it