Emails not appearing in Thunderbird for days but appear in Outlook without delay.

I have my gmail emails rerouted to my outlook email address and in past week my emails are not showing up in Thunderbird for a number of days after they are visable in my outlook program. Why? I have compared my Thunderbird settings with my partner and they are the same. Only difference is that my partner picks up her gmail email directly, does not use outlook and does not reroute her emails. She does not have any problems with emails arriving late to her Thunderbird inbox. We are both using same version. Any suggestions?