Rather than investing in expensive treats (which actually have to count as part of their veg and pellet allowance which together with any treat replace the supplementary role of wild forage in the mainly grass/hay fibre based diet they have evolved on), concentrate on making feeding time fun and encourage natural foraging behaviours and making them work for her normal dinner. It is both healthier and more stimulating for your piggies - and you, too, when you can't help giggling watching them.
Different hays and the occasional small portion of speciality hay is a healthier way to enrich the 75-80% of their daily food intake and to make their 'daily bread' a bit more interesting as well without it counting towards the veg/pellet/treat allowance.
Keep in mind that a modicum of preferably green veg with some occasional fresh herbs, one 1 tablespoon per piggy per day and any additional treats should not make more than a fifth to a quarter of what a piggy eats in a day. Since calcium doesn't evaporate, any dried treats are somewhat higher in calcium, so while they are good enrichment they should be used in moderation.
Pet store treats are generally highly processed and very often contain ingredients that should be avoided. A bit of dried forage plants sprinkled over their hay every now and then is a healthy way of treating. Especially if you provide some soft hay to burrow in or serve speciality hay in a toilet roll coardboard inners (if you have a very greedy piggy whose head could get stuck, just cut lengthwise through the cardboard. Also cut any handles of brown paper bags you can use for enrichment purposes.
A Comprehensive Hay Guide for Guinea Pigs (incl. providers in several countries)
Enrichment Ideas for Guinea Pigs