Gluten-Free and Lactose-Free are on the menu, but the same kitchen also prepares what you avoid, so cross-contamination is possible. Tell staff what you react to, and ask how your dish is prepared before you order.
The site describes Die Eisperle as a vegan ice cream maker in Graz that makes its ice cream and sorbet by hand in its own manufactory. It says the ice cream and sorbet are lactose-free and that gluten-free variants are possible. Tell the staff about your allergies, the kitchen has the final word.