Sound question. Adobe Connect and MacBook Pro.

A colleague will be presenting a webinar using a MacBook Pro and I will be facilitating from our office.  This is the third in a series she is doing and we have had no problems in the past.  However, when we did our dry run yesterday I could hear her but she could not hear me.  She is currently travelling in Europe, so I tested the sound on another colleague's laptop (also a MacBook) and there were no problems.  Any ideas as to why my colleague in Europe could not hear me?  She said her speakers were on and she was not using a headset.