u/yodaair

Hi, I will be asking a regular stylist to apply henna to my hair (Rainbow Brand) since finding it difficult to apply it myself. It is about 20 mins away. Should I premix henna with warm water and salt and then take it in an insulated bag in a Pyrex glass container? I'm thinking maybe I will take a small portion and premix it at least for the first appointment since I'm not sure if the particular stylist may find henna messy or thick to apply so a small portion may be better. Has anyone done this before and any special things to mention to a stylist who may not regularly work with Henna or advice on whether to have them mix it there or premix it myself. I'm in US. Thanks.