practice the basic recall with the lead on, and dont let her off until she understands. You could use a flexi lead/long tracking lead, or even some washing line attached to her lead, and let it get longer, telling her to sit and wait, walking away from her, then calling her, and making a big fuss when she does it right. 5 months can be a little young to expect her to come back when called as she is so excited to be in the outside world and wants to investigate, and going back to mom is boring, she probably thinks it is a game when you chase her around too.
Are you taking her to dog training?