hi,
i am currently house training my new 8 week old rottie pup vegas, so i completely know what you mean. it can be very frustrating!

even though you have got an older dog, you can still revert back to toilet training sprays, the simple solution toileting spray will help her toilet outside. just spray it on the ground and when she smells it she will want to go to the toilet. make sure she sniffs it, if she doesnt, just be patient and when she goes for a wee praise her and then reward her with a treat. you can continue doing this when you let her out to toilet, this may take a few times for her as it will be all new again, but dont worry she will get it. just remember positive reinforcement and treats when she does what you want her to do. when she knows to wee outside and she gets a treat then she will eventually do poos outside as well, again when she does this use positive reinforcement!

she will eventuall get it again, you just need to be consistent and patient with her. if she sees you are unhappy and frustrated when she is outside in the garden not doing what you want her to do, then she will learn that the garden is not a good place and she wont go to the toilet because of this. try to be calm and assertive and try not to get frustrated with her, she will learn quicker if you are on a good level when you take her out!

hope this helps, let me know how she gets on.
if you need any more help then please ask and i will try my best to help!