Hi @BrigidMcL 

1. If she was already in the list, she wouldn’t get the welcome email with the discount if she signs up again. To solve this (and if you want to offer the discount to people who are already in your list, you can setup a flow with the metrics “Form completed by profile” and put on a filter on the flow stating that they have been in your list for more than XX days. 
2. If she just subscribed, there could be numerous reasons as to why she has not received the email. If you look at the activity log for the event of her signing up and Klaviyo sending the email. Sometimes it is due to a full inbox for example.
3. If you have double opt-in on your list, she has to confirm this in order to receive the welcome message and discount.
4. If it was for some reason skipped, you can go to “View messages” in the top right corner of her profile in Klaviyo and see the message and then press “Resend”

I hope you find a solution!