Problem with mobile

Hi, Could you have a look on this page : http://www.penelopemilner.net/
The megamenu work perfectly over a width of 960px, under it’s not working at all.
Can you help.
Is there a way to disable it under a certain width and to let the theme menu take over in case we can’t manage to make megamenu working
Regards

https://wordpress.org/plugins/megamenu/