Is an email ok or improper?

My sister is staying with me. I have some things I want her to change while she's with us. I needed to talk to her since Saturday night but either she or I have been away from home. Tonight will be the same. I composed this long email outlining what we expect of her but now I feel like I should really talk to her. But I don't want to forget or leave something out. Or, worse, start a big argument and not get my point out, least of all across.