what age is she? If she is under 1 then she needs formula of some sort, whether it is soya or one of the other dairy free formulas. If she is over 1 then she can have soya milk or one of the other dairy free milks you can get e.g. oat milk. I doubt there are sugar free brands - they probably need the sugar for flavouring plus cows milk itself has sugar in it (lactose is the milk sugar). Better to have sugar than artificial sweeteners anyway.
Soya milk is also sweetened with apple juice concentrate I believe. But is available as sweetened and unsweatebed. Your local holland snd barrat should stock this. As do many supermarkets. As said above under one she will need a formula but alpro 1+ is suitable for ages 1-3 and my dd2 loves it. Kara coconut milk is also a good substitute. Oatly really doesn't contain enough fat or calories to be a drink suitable for a toddler and rice milk not safe under four
You can get unsweetened or sweetened soya milk at the main supermarkets and all seem to do their own cheap (Basics/Everyday or whatever they're called ranges). They don't seem to be any different from the standard ranges in taste or calcium/added nutrient content. Holland and Barrett are very expensive for soya milk. Unsweetened soya milk is pretty awful though - we used to give DS, who has a dairy allergy, a mixture of half and half sweetened and unsweetened for a drink but use unsweetened on cereal and in cooking. He now has Alpro almond milk for a drink (and soya on/in food) but I've just read the carton and it says it can be given from 1 year but shouldn't be the main milk drink before age 3.