My son has dust mite allergy and it’s variable due to the levels of dust. If she hasn’t cleaned so much that day or it’s been gathering whilst she is away, or she’s been disturbing stuff by moving it around, it’s a really hard one to have because even after a thorough clean dust always exists at a microscopic level and is not actually based on cleanliness.
So an allergy test will make her aware of the allergy but it’s not gonna cure it.
Maybe she will stop saying she has hayfever as she definitely doesn’t have that
or more likely she will say she’s reacted to them all