Can an establishment tell a patron Not to check their blood sugar levels or take their insulin?

Oh she was the rude one! You should absolutely be able to test and inject wherever you want. In fact, a bathroom might be worse because it could be dirty and unsanitary.

I think you have the right to talk with her manager cause she didn't had any consideration with you what so ever. I am diabetic too I knew about it 4 months ago and I get embarrassed everytime I had to check my sugar level or put some insulin infront of people. But like a friend told me if they don't like it then they shouldn't look at it so I took that very serious and I really don't care anymore. For us diabetic is very important to do everything to matai our sugar level normal so because she doesn't like it, it doesn't mean everyone is the same way.

She can tell you, but she can't force you. She's also incorrect. There's no health danger to anyone in the room or you if you test your blood sugar or inject insulin. Whether you're in the bathroom or a living room, the same rules apply: clean needles, clean lancets, clean hands, and so on. Others being there doesn't change anything. In fact, I'd argue that you're probably safer injecting or testing outside a bathroom, especially a public bathroom where you'd have to touch a stall door and latch after washing your hands. I'd say that she's simply uncomfortable watching it, much like watching a woman breastfeed, and that she feels she has the right to intrude. She might be justifying the intrusion because she plans to become a nurse. It's your call on how to handle it, but if certainly if she continues pressing the issue, it's time to talk to her about diabetes management because she clearly doesn't know very much.

I'd ask for the manager immediately and remind the manager that it's illegal to separate a diabetic from their supplies or their procedures. Whether or not I file a complaint would depend on the managements measures. The truth is, most people won't notice a glucose test or injection unless they knew what it was for and then they would be quite accepting of it.