Most doctors would recommend to skip any medication if you try to get pregnant. While there is no strong evidence for severe harm due to psychostimulants you cannot exclude any risk. I am not aware of any adhd meds without this little (but important) risk. The good information : Most women report less severe symptoms of ADHD while they are pregnant. This is caused by hormonal changes that have a positive effect.
In Germany some psychologists use EEG-Neurofeedback to cope with ADHD symptoms if you are not allowed to swallow pills for ADHD. This might be an option for your wife if it is available in your region.
It might also be a good option to join an ADHD self-help group in your town. To talk about your problems with other women is a very good option to cope.