How likely is ocular melanoma in a 16 year old?

I took my daughter for an eye test yesterday, she had one last summer too. Yesterday they told me they were going to refer us to hospital because she has a ‘small discolouration’ at the back of her eye. I was taken aback honestly and didn’t have a clue what that meant so i obviously googled when I got home and saw melanoma. The hospital rang me today, and said they want to see her in clinic and they will send a letter through with an appt. I asked how long it would be, and he said between 4-6 weeks. I didn’t get much sleep last night, I had a little cry because I’m scared, and worried a lot with lots of broken sleep.

How worried should I be?