Why won't my Bluetooth speaker work with Skype

The volume on my tablet is not loud enough for my stepmother to hear when receiving calls on Skype. I've paired it with a Bluetooth speaker and it plays music etc fine but when receiving calls through Skype, they don't go through the speaker. Skype say you can change this through the tools and options menu, but there isn't one on the tablet. Any help would be very much appreciated.