Hi KK
Diabetic clients should all be treated as individuals. In general she may have some neuropathy issues - reduced sensation in extremities (hands and feet), fragile skin and slower wound healing and perhaps underlying health issues which may mean she’s more likely to have a dizzy spell after lying down for a period of time or possibly to be unsteady on her feet or a bit clumsy or disoriented.
Add in the recent heart attack and I wouldn’t lie her flat, flat for a facial, I’d prop her slightly with pillows or bolsters under her feet/knees and the couch slightly raised at the head (lower the couch so it’s easier for you). You should make sure she’s comfortable and pay particular attention to temperature, touch her feet to see if they are warm (a well wrapped hot water bottle with hot tap water rather than boiling water may be appreciated). I’d keep treatment times on the shorter side - 45 mins for a first facial rather than an hour and maybe a warm compress rather than a steam.
There are no real no nos other than to avoid anything that might damage the skin - so no microdermabrasion or extractions. You should stay within your training but you should be safe with aromatherapy massage (avoid hot stones). You can use your judgement over brows and waxing - check the skin, don’t do on a very hot or cold day, give advice to stay out of the sun afterwards.
Hair can be weak or thinning so I wouldn’t offer lash extensions but I would do lash lifting after I knew the client well and deemed it safe.
Pampering after a health scare is really nurturing and helps restore confidence and wellbeing so try and find a way to say yes, just do as you have done and play cautious.
Regarding a pedicure I wouldn’t discount as it will feel like a cut price service, instead find ways to replace the value of the gel application time. Looking after feet is really important so offer a longer soak in lovely bath salts with a dash of aromatherapy oil. Use a nice scrub unless the skin is really fragile. Slosh on a foot mask on one foot whilst you massage the other. And give extra massage it will feel amazing and there isn’t really a reason to avoid doing. Make the in between gel application pedi about the foot care making sure the toenails are filed smooth and are not too short nor too long and keeping on top of hard skin using nice creams rather than aggressive foot filing.
Your client will really appreciate your care and attention. I have a client with lymphoedema in her legs. I can’t massage her but she adores having me gently smooth her skin with nice creams. She always tells me I’ve done her good, so trust in your ability to personalise a treatment to your client’s needs, don’t reduce the service and offer a discount just because you feel you haven’t done much.