How do I proof whatsapp isn't installed on my tablet

This might be a strange one but I need to proof whatsapp isn't installed on my tablet but more importantly that it hasn't been used on that number in the last few months..
The girlfriend is convinced I sent a message to an ex girlfriend ( who is still a friend ) and included heart and kisses emojis , she is also convinced that I somehow deleted the emojis using photoshop etc and somehow planted them messages back on the exs phone....all crazy I know but I would love to proof to her that whatsapp hasn't been used on my tablet....ive asked whatsapp but they aren't responding to my emails

So any simple way to proof I haven't sent any messages on my tablets whatsapp

Thanks

Thanks but it's not quite that simple , the story was.....
I was sat with the girlfriends daughter and got a whatsapp message on my phone I replied a short message I'm at girlfriends and after a couple of short messages the conversation was over......the next day after I get home the girlfriend sends me a message asking what I was doing on whatsapp at such a time and after a couple of text messages its all over and im single again, I speak to her the following morning and the accusation is....the daughter is adamant that I sent the messages on my tablet and she asked who X was and that the message had heart and kisses emojis...
After the conversation I immediately went into the office where my ex works and took a photo of her phone with the said conversation....no emojis of course.
I see the girlfriend a few days later and she gives me a load of crap about how you can do all sort of things to whatsapp and is convinced somehow I have doctored it, the bottom line is that whatsapp isn't installed on my tablet I just need to prove that the tablets number isn't registered or hasn't been used for whatsapp in the last month..
And yes before you ask she's been hurt big time in a previous relationship and im getting that insecurity...
Sorry about the long message I just need to pin this down...

Thanks Lindsay, I'll keep emailing WhatsApp and see if I can get anywhere , and yes I know but you can't help who you fall in love with can you, I worked with the ex and still do occasionally so we just remained friends I've been totally honest and upfront with the new one and she has known about it from day one, I'll just have to hope she gets over the memories of the loser that did the dirty on her ....