I think I can help
I made my second batch and omitted the 3rd bottle of lemon because we both have acid reflux.
After it was done, I simmered 7 pounds of frozen mixed 4 berries down to extract the juice. I also have a couple of over ripe bananas and put them in with the berries. I then allowed it to cool, put all the skeeter pee back in the the pail and added all the berry juice. It is awesome.
The first batch I used 64 oz bottles of juice that was all natural and no sugar from the juice aisle in Wally World. I then simmered down the juice to about half to remove the water and added that to 1 gallon carboy and then filled with skeeter pee.
For the first batch I used the juice.
The juices I used for each gallon were
cranberry
black cherry cranberry
blueberry
strawberry banana
peach mango
Our favorites were the cranberry and black cherry cranberry. Everyone raved about those 2. The blueberry is good also.
The 3rd batch of skeeter pee is in the works now. And they will be mostly cranberry and black cherry/cranberry. I started with only 15 oz of lemon, and 15 oz of lime and will not add the 3rd bottle. I used a quart and a pint from the 4 berry and it took off 12 hours after I added the slurry. I posted a photo a few posts down too.
A few posts down, I posted a photo of the 4 berry pee.
So with your frozen strawberries, you could simmer them, no sugar added, squeeze the bag of fruit and add it your pee when it has cooled down.
I too have strawberries in the freezer that I had planned to make strawberry wine but this last batch of pee, I will make some strawberry too.
Make sure you sweeten as per the end of the recipe and to add the sorbate, kmeta or campden before you add the juice.
Hope this helps