Potty training please help?

my little girl is 20 months, she tells me when shes done a poo but not a wee, she loves sitting on her potty and will sit there and watch dora or share a book and by which Point she normally wee's. she can pull her nappy down and has been understanding and following directions for a good few months. so i figured t was time to try. so i have had her in knickers around the house and every time she wets her self she grabs her potty, comes over to me and crys but she cant seem to recognise before she needs to go. should i stop and wait and try again in a months time?