Please look at your situation through a different point of view for a minute. By letting a kid play in grass, by letting a kid pee behind a bush, by spending time in the truly GREAT outdoors, you are giving your kid a priceless gift. They learn to love nature, they breath fresh air custom made for living beings, they learn to adapt to the needs of the moment, they learn we don't have to be surrounded by "civilization" to get on. Those are not things every kid is blessed with. You were making good choices.
If you were given frequent accurate warnings that outside is bad and still let them play outside, then you could justify guilt. Outside is not bad. We need a way to keep playing outside , but without fear. Vacines, repellents, vector controls, cures - something to fix the problem at the root. Mice don't get sick from the tick according to a new headline - perhaps that will help lead us to good answers.
Meanwhile, you are in the uphill battle between trusting yourself and trusting your doctors. There is no easy answer there. If you keep reading, and asking around, and consulting with llmd's who don't deny Lyme as an ongoing problem, you are doing your job as defender of your children.
When my son lost his peripheral vision in one eye the head eye doc, 3rd to see him for it, decided he was faking it. Fortunately I had an out of coverage second opinion that disagreed. Regardless of if it was 'real' or not, a neuro and an ID saw him next, at my insistance (ence?). Although I still could not get a lyme diagnosis, he did get 'encephalopathy'. He was given Amoxicillin, and magnesium. His vision had already returned so I think they were trying to quiet a very squeeky wheel. Perhaps they were covering their rears.
I am mom, hear me squeak. And squeak. And squeak. (Like an infected white footed mouse?)
If you keep pushing for answers and keep up the hope and don't give up you will be the best advocate she can have.