Asthma and/or wheezing in itself is not a problem for conception and pregnancy.
I would suggest that as per best clinical practices, it is better to use anti-asthmatic medications by inhalation rather than by oral route. Very little medicine gets absorbed into the body system when taken by inhalation thus reducing side effects. For example Asthalin (salbutamol) is also available in inhalation form.
Selection of most appropriate and relatively safer medicine is also very important. For example salbutamol (Asthalin) crosses placenta and reaches the foetus. Due to obvious ethical reasons, clinical trials to determine the safety and efficacy of salbutamol during pregnancy have not been conducted. However large doses in animals were found to result in the birth of deformed offsprings. The relevance of this animal studies to humans is not known. It is recommended that salbutamol during pregnancy should only be used if the benefits clearly exceed possible risks. The US Food and Drug Administration (USFDA) has categorized salbutamol as Category B.
Terbutaline (trade name: Bricanyl Misthaler) via inhalational route is similar to asthalin but its has been categorized as A by USFDA i.e. safe during pregnancy.
The patient should naturally avoid taking chocolates and keep away from dust to the extent it is possible so that minimal medication is required.
No treatment is necessary before conception.